The steady increase in demand for power sources, the climatic changes caused by heating of the atmosphere and the easily extracted oil reserves, along with a more intense socio-economic development, especially in developing nations, has provided incentive for the consumption of renewable resources, which can at least partially substitute fossil fuels such as oil, coal and natural gas.
Recently, biodiesel arose as a viable alternative in terms of renewable fuel. Transesterification is currently the most commonly used process in biodiesel production. It consists of a chemical reaction of vegetable oils or animal fats with common alcohol (ethanol) or methanol, stimulated by a catalyst, of which also extracts glycerin, a product with many different applications in the chemical industry.
Biodiesel may also be attained through other processes such as cracking and esterification. From a chemistry point-of-view, the oil or fat is used in the production of biodiesel is a triglyceride, that is, a tri-ester derived from glycerin.
Under the action of a basic catalyst and in the presence of methanol of ethanol, the oil undergoes transesterification, forming 3 methyl ester or ethyl molecules from the fatty acids, which constitute biodiesel in its essence, and liberating one molecule of glycerol or glycerin. Dozens of plant species may be used for the production of biodiesel, such as castor, palm, sunflower, babassu palm, peanut, soybean and jatropha, among others, as well as animal fats (e.g., tallow) or vegetable.
The processes for biodiesel production generally have a maximum mass yield of 95%, primarily depending on the quality of the fatty material. The better the quality, the higher the yield. Generally, the higher quality raw materials are more expensive, making biodiesel production economically unfeasible. The low mass yield is another economically negative aspect that ends up impacting the business profitability.
Triglycerides with high acidity are normally esterified prior to proceeding with the transesterification step. The process of esterification is a costly step because it requires that the excess methanol used and the reaction water be eliminated via the process of distillation, which increases the cost of the production process.
Crude glycerin coming from the current process lose around 5% to 10% of fatty material in form of 25 esters, partial glycerides and soaps, hence the final yield is around 95% at most. To separate the fatty material contained in crude glycerin, inorganic acids are usually added, such as sulfuric acid or hydrochloric acid, with the formation of their respective salts.
The glycerin generated has a purity of 60 to 80%, however the major drawback is the presence of inorganic salts like sodium sulfate and sodium chloride, which makes the glycerin purification process costly and introduces corrosion problems in the equipment used to distill the glycerin. The use of this glycerin as such is very limited due to the presence of these salts. Besides this productive aspect, a large amount of solid residue is formed, which needs to be discarded into the environment. With all these negative aspects, the value of this glycerin is marginal, and currently is a problem for major biodiesel producers.